Sea lion predation at record level

The number of sea lions and the number of salmon they’ve eaten this year in the Bonneville Dam tailrace is more than double the twelve-year average, according to a May 12 status report by the U.S. Army Corps of Engineers.

Sea lions, or pinnipeds, have caused havoc this year, both at the dam where they pick off salmon and other fish stalled in the tailrace, and lower in the river where commercial and recreational fishing has been impacted, as well as in Astoria where sea lions have taken over docks.

At the dam, their presence has broken records for the number of sea lions observed in one day and for the number of chinook salmon eaten over the season.

Both the home-grown Steller sea lions and the California sea lions have been picking off salmon at the dam since January and February, but April is the record setting month for their numbers and their carnage, according to the report.

Steller sea lions were present when the first observations were made January 13 and their numbers have been building as has the run of spring chinook salmon they are eating. In one day, on April 22, 69 Steller sea lions were observed at the dam, a new single day record for Bonneville eclipsing the 53 Steller sea lions observed in one day in 2010.

Some 53 unique individual Steller sea lions have been identified. Thirty-three were repeat individuals (they had been observed before), 15 of those had been branded, and 20 may be new to Bonneville.

California sea lions began showing up at Bonneville February 9, with the highest number on April 29 when 62 were observed in the tailrace. That number is also a record, eclipsing the old record of 52 set in 2007. Observers have seen 129 branded California sea lions this year. Twenty-four of those had been observed in prior years, 26 were brands not seen before at Bonneville, and 79 were trapped and branded.

Overall in 2015, the daily average number of combined pinnipeds observed in the dam’s tailrace in January was 12, eight in February, 22 in March and 78 in April. So far in May, the average is 76 per day.

The highest number observed for both pinniped species combined was 116 on April 22, a new record for Bonneville. The previous record was 71 per day set in 2010.

Given the number of sea lions present at the dam and the number of adult spring chinook salmon passing the dam (as of May 10 that number was 173,264), it’s not surprising that the sea lions are taking record numbers of fish.

All pinnipeds took a total of 4,108 chinook salmon and 110 steelhead. That’s just the observed take. Add in an estimate of unobserved take and the total for both salmon and steelhead is 5,879 fish, more than twice the cumulative average over the years 2002-2014 of 2,766 salmon and steelhead.

Of the observed catches, California sea lions took 2,968 chinook salmon and 20 steelhead, while Steller sea lions took 1,140 chinook and 90 steelhead. Pinnipeds were also observed to take 22 Pacific lamprey, 13 American shad and 392 other or unknown species.

The white sturgeon take has been low at 23. The average for the years 2006-2014 has been 1,284 white sturgeon through May 6, the effective date of the May 12 report.

The Corps and other agencies and tribes are taking measures to reduce sea lion predation with sea lion exclusion devices installed at fishway entrances and some powerhouses, as well as boat-based harassment by the Columbia River Inter-Tribal Fish Commission that began March 6 and will continue to the end of May. Dam-based harassment that began on March 18 by the U.S. Department of Agriculture is conducted seven days a week and will also continue through May.

Other management activities by the Oregon and Washington fish and wildlife departments have euthanized 14 California sea lions and trapped, branded and released 79 in 2015.

While efforts to keep sea lions away from the dam’s tailrace continue, the efforts have not been without mishap. Two California sea lions died accidentally when they were crushed by a much larger sea lion in a crowded trap during the week of April 27 and one Steller sea lion died when it was accidentally caught May 4 between two traps and drowned.